1. Field of the Invention
The present invention relates to an information recorder/reproducer which compresses video signals for each basic unit of one field or one frame so that the compressed video data are recorded on or reproduced from a plurality of tracks on a magnetic tape per basic unit.
2. Discussion of the Related Art
Conventionally, video signals are inputted to a generally utilized helical scan-type information recorder/reproducer (hereinafter referred to as a VTR) which scans in a helical manner with a magnetic head attached to a rotating cylinder and, thereby, the data thereof are recorded on a magnetic tape. In this case, since video signals of one field are, conventionally, recorded on one track, the recording is carried out by changing the number of revolutions of the rotating cylinder or by changing the transfer speed of the magnetic tape in accordance with the difference of the frequency of the vertical synchronizing signal due to a broadcasting system such as an NTSC system or a PAL system. In addition, at the same time, control signals are recorded corresponding to each track in the longitudinal direction of the magnetic tape by means of a fixed head.
In order to make the phase relationships between the tape transfer at the time of reproduction and the revolution of the rotating cylinder correspond to the relationships at the time of recording, control signals and FG signals are used. An FG signal generation circuit generates signals which are proportional to the number of revolutions of the capstan and the frequency thereof is proportional to the transfer speed of the magnetic tape. At the time of reproduction the control signals are reproduced by the fixed head so as to count the FG signals generated within a period of the control signals. By comparing this measurement result with a predetermined value, the broadcasting system of the recorded program can be determined.
On the other hand, in the case of an information recorder/reproducer such as a digital VTR, the inputted video signals are compressed for each basic unit of one field or one frame and the compressed video data are signal converted and given to the magnetic head of the rotating cylinder so as to be recorded in a plurality of tracks per basic unit. At this time, in order to minimize the difference in the signal processing between the NTSC system and the PAL system, there is a method for making the number N of tracks for recording per basic unit be of a ratio of NTSC:PAL=5:6. According to this method the number of revolutions of the rotating cylinder and the transfer speed of the magnetic tape can be made approximately the same.
For example, in a method for changing the number N of tracks per basic unit in accordance with the difference in the broadcasting system, such as in a digital VTR, the number N of tracks used for one frame is made to be 5n or 6n (n is a natural number) in the NTSC system or in the PAL system, respectively, in the case that the basic unit of the compressed video data is one frame. FIGS. 1 and 2 show the relationships between the frame signals as well as head switching signals (HSW signals) and the track tracing in the case of n=2. In the NTSC system shown in FIG. 1, the frame period is 33.366 ms. In the PAL system shown in FIG. 2, the frame period is 40.000 ms.
In the NTSC system, when video data are recorded in ten tracks 43 by using a magnetic head attached to a rotating cylinder during one period of the frame signals 41, HSW signals 42 for switching the magnetic head are switched in polarity thereof for every 3.37 ms. In the PAL system, when video data are recorded in twelve tracks 44 during one period of frame signals 41, HSW signals 42 are switched in polarity thereof for every 3.33 ms. That is to say, the ratio of the number N of tracks for recording per one frame of the NTSC system to that of the PAL system is made to be 5:6, the ratio of the number of revolutions of the rotating cylinder and the transfer speed of the magnetic tape becomes (1.000:1.001), which is approximately the same.
In such an information recorder/reproducer, as well, control signals are recorded by a fixed head in the longitudinal direction of a magnetic tape. When the control signals are reproduced by the fixed head, however, the counted value may differ by only 0.1% even in the case that the FG signals outputted by the FG signal generation circuit within one period of the control signals, that is to say, the pulses of the frequency corresponding to the tape speed are counted. Accordingly, there is little difference between the broadcasting systems concerning the number of revolutions of the rotating cylinder or the transfer speed of the magnetic tape. In such a method, however, there is the problem that the broadcasting system of the video signals recorded on a magnetic tape cannot be specified.
The present invention provides an information recorder/reproducer which records, on a magnetic tape, video signals having the number N of tracks corresponding to a broadcasting system for each basic unit of the video and control signals corresponding to each track. The information recorder/reproducer according to the present invention has a capstan for transferring a magnetic tape in the longitudinal direction, an FG signal generation unit for outputting FG signals that are proportional to the number of revolutions of the capstan, a fixed head for recording or reproducing control signals on or from positions in the longitudinal direction of the magnetic tape corresponding to each track and a recording control signal generation unit for generating control signals, of which the duties differ for every N tracks, corresponding to each track and which are outputted to the fixed head. In addition, the device has a control signal amplification unit for amplifying differential control signals reproduced by the fixed head, a waveform formation unit for generating CTL signals which differentiate a positive polarity to negative polarity section from a negative polarity to positive polarity section in one period of the differential control signals amplified in the control signal amplification unit, a CTL signal duty ratio determination unit for detecting the duty ratio of a positive polarity to negative polarity section to a negative polarity to positive polarity section in one period of the differential control signals from CTL signals outputted from the waveform formation unit and FG signals from the FG signal generation unit, a CTL signal counting unit for counting the number of outputs of the CTL signals obtained by the waveform formation unit, and a broadcasting system determination unit for determining the broadcasting system of the video signals recorded on the magnetic tape based on the outputs of the CTL signal duty ratio determination unit and the outputs of the CTL signal counting unit.
The number of tracks for a basic unit has been decided in advance in accordance with the broadcasting system and the video signals can be determined by recording and reproducing the control signals of which the duty ratios differ for each number of tracks.
In addition, in this information recorder/reproducer, in the case when the number N of the control signals recorded in one frame or in one field of the magnetic tape for each basic unit of the video is 5n (n is a natural number) in the NTSC system or 6n in the PAL system, the broadcasting system determination unit determines whether the CTL signals which have a predetermined duty ratio recorded in the border of one frame or one field are inputted for every N=5n or for every N=6n based on the determination result of the CTL signal duty ratio determination unit and the counted value in the CTL signal counting unit so that the broadcasting system can be determined to be the NTSC system in the case of N=5n and can be determined to be the PAL system in the case of N=6n.